Ultrasound machines are often used for observing organs in the human body. Typically, these machines contain transducer arrays, which are comprised of a plurality of individually excitable transducer segments, for converting electrical signals into pressure waves. The transducer array may be contained within a hand-held probe, which may be adjusted in position to direct the ultrasound beam to the region of interest. Electrodes are placed upon opposing portions of the transducer segments for individually exciting each segment. The pressure waves generated by the transducer segments are directed toward the object to be observed, such as the heart of a patient being examined. Each time the pressure wave confronts an interface between objects having different acoustic characteristics, a portion of the pressure wave is reflected. The array of transducers may receive and then convert the reflected pressure wave into a corresponding electrical signal.
Two-dimensional transducer arrays are desirable in order to allow for increased control of the excitation along an elevation axis, which is otherwise absent from conventional single-dimensional arrays. A two-dimensional transducer array has at least two transducer segments arranged along each of the array's elevation and azimuthal axes. Typically in a two-dimensional transducer array there are 128 transducer segments along the array's azimuthal axis and two or more segments along the array's elevation axis. As a result of the two-dimensional geometry, one is able to control the scanning plane slice thickness for clutter free imaging and better contrast resolution.
It is desirable to form high density two-dimensional transducer arrays because they are compact and may provide clearer images. However, prior art high density two-dimensional arrays are typically difficult to fabricate because the width of the transducer elements is generally 50 to 100 .mu.m. In order to produce a high density two-dimensional transducer array, many leads or traces are soldered to the small individual transducer segments in the array in order to provide the appropriate electrical signals for excitation. Thus, on a typical two-dimensional transducer array, hundreds of traces must be soldered to the respective segments to effect excitation.
As a result of the high density form of the arrays, prior art two-dimensional transducer arrays typically have unreliable lead attachments to the respective transducer segments. The dimensions of the segments are small and the connections between the traces and the transducer segments may fail. In addition, the traces and solder connections are subject to heating and cooling and may not withstand the temperature changes. As a result, these connections may break apart. Yields as low as 10 percent for producing high density two-dimensional arrays are not uncommon. Consequently, prior art methods for constructing high density two-dimensional transducer arrays have generally been complex, unreliable, and cost prohibitive from a yield point of view.
In addition to the problem of unreliable lead attachments, typical prior art transducers operating at higher frequencies with the larger elevation aperture of the two-dimensional array will clutter imaging in the shallow portions of the human body. It is desirable to image regions deep within the human body at higher frequencies, while maintaining the ability to generate clear near-field images. Generally, higher frequency transducer arrays having a smaller elevation aperture are used to improve the resolution of sectional plane images of shallow regions within the human body.
Higher ultrasonic frequencies, however, are more quickly attenuated in the human body. Therefore, in conventional ultrasound systems, lower frequencies of ultrasonic waves are generally used to improve the resolution of sectional plane images of deeper regions within the human body. Nonetheless, clearer images of deeper regions within the human body may be generated if the transducer array is capable of providing higher ultrasonic frequencies from an expanded or larger elevation aperture while also being capable of maintaining clutter free near field images. Clutter free near field images may be produced if the same transducer array is capable of providing higher ultrasonic frequencies from a smaller elevation aperture (i.e., switching-in a smaller elevation aperture).